Trying to do too many things, including helping others fault find existing (old) boards…
When looking at digital waveforms, I normally make the following recommendations:
- For high speed signals, use a X10 scope probe (and calibrate it using the test signal available on many scopes by adjusting the adjustment trimmer for the best waveform, that is minimum overshoot/undershoot and the best square wave),
- Show on the screenshot or photo where 0V/GND is in relation to the displayed waveform.. If possible mark the volts per division as well as the voltage measured by the scope.
- Use a good 0V/GND point for all the ‘scope probes.
Can you please double check that it’s fitted the correct way round.
By the way, the purpose of C67 is to try to speed up switching on and off.
If TR3 is fitted correctly, the options as I see it are:
- Try another PH2369
- Try a lower resistor for R24. However, a 1kΩ should be fine for this design.
- Try a different transistor.
The selection of the resistor is a compromise, a lower value increases the base current and turns the transistor on harder, it also which increases the saturation of the junction, which in turn increases the amount of time it takes to turn off.
A higher value reduces the amount of current to the base of the transistor, which means it’s junction is less saturated, so it should turn off quicker. But you still need enough current to turn the transistor fully on so that the collector goes to near 0V/GND.
Mark